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The Apache Software Foundation has released fixes to contain an actively exploited zero-day vulnerability affecting the widely-used Apache Log4j Java-based logging library that could be weaponized to execute malicious code and allow a complete takeover of vulnerable systems.

Tracked as CVE-2021-44228 and by the monikers Log4Shell or LogJam, the issue concerns a case of unauthenticated, remote code execution (RCE) on any application that uses the open-source utility and affects versions Log4j 2.0-beta9 up to 2.14.1. The bug has scored a perfect 10 on 10 in the CVSS rating system, indicative of the severity of the issue.

“An attacker who can control log messages or log message parameters can execute arbitrary code loaded from LDAP servers when message lookup substitution is enabled,” the Apache Foundation said in an advisory. “From Log4j 2.15.0, this behavior has been disabled by default.”

Exploitation can be achieved by a single string of text, which can trigger an application to reach out to a malicious external host if it is logged via the vulnerable instance of Log4j, effectively granting the adversary the ability to retrieve a payload from a remote server and execute it locally. The project maintainers credited Chen Zhaojun of Alibaba Cloud Security Team with discovering the issue.

Log4j is used as a logging package in a variety of different popular software by a number of manufacturers, including Amazon, Apple iCloud, CiscoCloudflare, ElasticSearch, Red Hat, Steam, Tesla, Twitter, and video games such as Minecraft. In the case of the latter, attackers have been able to gain RCE on Minecraft Servers by simply pasting a specially crafted message into the chat box.

images from Hacker News